Coated objects



Patented Sept. 6, 1938 to EII. du Pont de Nemours & Company, Wilmington,Del., a corporation of Delaware No Drawing.

Application June 2, 1936,

Serial No. 84,232

13 Claims.

This invention relates to coated articles and their preparatiom'and moreparticularly to coated articles having under the coating 9. priming coatcomprising deacetylated chitin.

The present application is a continuation in part of copendingapplication Serial No. 11,320, filed March 15, 1935, which has issued asU. S. Patent 2,047,220, which is hereby incorporated herein.

Chitin is the chief component of the horny exoskeletons oi crustaceasuch as shrimp, crabs, or lobsters. According to currently acceptedtheories, it is a polymer of an-acetylated glucosamine. A method hasrecently been developed by George W. Rigby (U. S. Patent 2,040,879) forthe chemical treatment of chitin with alkali under controlledconditions, whereby chitin is deacetylated to the extent that it becomessoluble in dilute aqueous acids but not to the point where the chitinmolecule is so changed or degraded that the product is incapable ofbeing formed into coherent films. acetylated chitin, is the one which Iuse in my present invention, and by the quoted expression I imply aproduct which is soluble in aqueous acids and not degraded beyond thefilm-forming stage.

Rigid fibrous cellulosic materials used for construction purposes, suchas wood, are customarily given protective or decorative coatings such aspaint, enamel, lacquer, or the like. Due to the porosity of such basematerials, special priming coats or additional coats of the regularfinish must frequently be used to obtain good results. These arerequired to give full protection and/or to avoid the formation of lowgloss or non-uniform areas disfiguring the normal appearance of theproperly applied coating. Furthermore, even when properly applied,coatings frequently fail by blistering, peeling or flaking, especiallywhen the rear of the coated base is exposed to water.

This invention has as an object a process for the preparation orimpr'oved coatings on rigid fibrous cellulosic surfaces of the type usedas construction elements, such as wood. A further and more specificobject is a process for sealing and subsequently coating rigid fibrouscellulosic surfaces in such a manner that the adhesion to such surfacesof the finish coat is improved. A still further object is the improvedmulticoated article produced by the process. Other objects will appearhereinafter.

These objects are accomplished by the following invention wherein arigid fibrous cellulosic surface such as wood is coated with a so- Thisproduct, termed delution of deacetylated chitin in aqueous acid, thecoating is dried, and upon the coated surface thus produced there isapplied a finishing top-coat of an organic film-forming material,particularly one based on a drying oil or drying oil modified alkydresin. I have found that deacetylated chitin bonds strongly to wood andother types of rigid fibrous cellulosic surfaces used in the buildingindustry, and that many coating compositions adhere to it in turn underadverse and severe conditions. The result is a surface which isprotected to a greater degree than has heretofore been possible, as willbe apparent from the subsequent more detailed de scription.

As previously indicated, I use in my invention a. solution ofdeacetylated chitin in aqueous acid, which solution may if desired haveliquids or solids emulsified or dispersed therein. In all cases, it maybe said that I employ a water-soluble salt of deacetylated chitin in anaqueous menstruum. I prefer that the acid which is used to form thissalt be one which is volatile, such as acetic, propionic, or formic.When volatile acids are used, the intermediate coating of deacetylatedchitin is more readily rendered waterinsoluble.

In the examples which follow, reference is made to deacetylated chitinof difierent viscosities in poises. This is theviscosity of an arbitrarystandard, viz. a 5% solution in 5% aqueous acetic acid. Deacetylatedchitin is further arbitrarily considered to be of the low viscosity typeif the viscosity of the standard solution at 25 C. is in the range 1-35poises, of the medium viscosity type if the standard is in the range35-250 poises, of the high viscosity type if the standard is above 250pulses. In the present process all of these types may in general beused, but the type to be chosen for best results will obviously dependupon the particular effect desired. For maximum penetration andimpregnation, dilute solutions of low viscosity deacetylated chitin arepreferred. High viscosity deacetylated chitin is best for maximumsealing of the surface. Intermediate effects are obtained with themedium viscosity material.

As already stated, the present invention is generally applicable to thecoating, with concontain an inert material, preferably a finely dividedsolid, dispersed therein. To the deacetylated chitin primed wood surfacethere is then applied an organic film-forming material, especially acomposition containing or consisting of a film-forming polyhydricalcohol ester of drying oil acids, e. g., a drying oil or a drying oilmodified alkyd resin. In the case of drying oils, excellent results havebeen obtained with white lead in oil paints having no zinc oxide anddesigned for use outdoors. In the case of oil modified alkyd resins,good results are most apparent when the resin contains not more than 50%oil.

Having thus outlined the principles of the invention the followingexemplifications are added in illustration, but not in limitation.

Example I One-half of a pine board was primed by brushing on a 2 percent aqueous solution of the acetate of a medium viscosity grade ofdeacetylated chitin, the other half being left unprimed. After drying,the entire board was painted. Over the primed area the coatingcomposition dried to a gloss equivalent to two normal coats of the samepaint while over the unprimed area of the wood the paint was fiat andspotted. Similar results are obtained with other rigid fibrouscellulosic base materials such as various types of wood including cedar,White pine and yellow pine, synthetic wall-boards-used in the buildingtrade, cardboard, plywood, boxboard, corrugated paper, and the like. Theconcentration of deacetylated chitin solution required for purposes suchas that illustrated in this example will vary with the viscosity gradeof the deacetylated chitin, smaller concentrations of high viscositygrades being required than of low. As already indicated, penetrationinto the base de-' creases with increasing viscosity. Grades havingviscosities of 200-300 poises are in general to be preferred since 2-3per cent solutionsthereof in dilute aqueous acid are very efiective ingiving in one coat correct balance between sealing and penetration. I

Example II A wood surface badly stained by asphalt was painted with a 2per cent solution in 0.7% acetic acid of 300-poise deacetylated chitin.A paint coat subsequently applied was stained by the asphalt only on theportions of the panel not primed by the deacetylated chitin. Forpurposes such as that illustrated in this example the deacetylatedchitin of medium and high viscosity again is most effective. Toillustrate further, a 2 per cent so lution of a 200 poise deacetylatedchitin gave decidely better; results over wood than a more concentratedsolution of low viscosity deacetylated chitin, e. g., a 5 per centsolution of a 6-poise material. This sealing action of deacetylatedchitin is especially evident with wooden surfaces. However, a beneficialefiect is also secured over synthetic wall-boards and other rigidfibrous cellulosic construction materials. Not only does thedeacetylated chitin seal against asphalt but also against oil-solubledyes, creosote, andsimilar organic solvent soluble substances. It isuseful in the priming of highly resinous woods to prevent the unsightlyexudation of natural resins through the finish coat, and in sealingparticularly resinous portions, such as knots.

Paints applied to wood the 'back of which is subsequently exposed tomoisture frequently fail by blistering or peeling following loss ofadhesion. Paints applied to wood and exposed to the weather ofteneventually become hard and brittle, and they frequently lose adhesion asis evidenced by the paint cracking and flaking off. By this invention ithas been made possible to decrease the tendency of many coatingcompositions to fail in this way. In carrying out this part of myinvention, I apply, as before, a deacetylated chitincontaining primingcoat to the wood before applying the regular coating. In the exampleswhich follow illustrating this, the aqueous solution of deacetylatedchitin may optionally contain liquids or solids emulsified or dispersedtherewith.

Ewample III A very highly pigmented coating composition comprising partsby weight of extended titanium pigment and 20 parts by weight of 62%linseed oil modified alkyd resin was made up and applied to white pinepanels, some of them unprimed and others primed with 0.5 per centsolutions in acetic acid of medium viscosity deacetylated chitin. Thesepanels were exposed to severe weatherin conditions and examined forpeeling and cracking. When the coating on the control panel hadcompletely failed by peeling and cracking, that on the primed panel wasstill intact.

Example IV The latter were inevitably between enamel coats' rather thanbetween wood and paint. Over the unprimed wood the coating could bestripped on after steam treatment, but over the primed wood, it wasgenerally less difficult to separate one coat of paint from another thanto separate paint from primed wood.

Example V Dispersions of many finely divided solid materials indeacetylated chitin solutions are very effective for improving theadhesion or decreasing the blistering tendency of subsequent coatprising40 per cent of titanium dioxide and 2 per cent low viscositydeacetylated chitin (dissolved in acetic acid) was used as a primer fora 48.6% oil modified alkyd resin enamel. Severe accelerated tests showedonly slight failure over primed wooden panels but almost completefailure on controls, 7

Instead of the titanium dioxide of Example V other finely dividedrelatively inactive solids or mixtures such as extended titaniumpigments, zinc sulfide, lithopone, barytes, blanc fixe, aluminumstearate, asbestine, antimony oxide, silica, 'milori blue, chromeyellow, carbon black, or mixtures such as lithopone, mica and extendedtitanium dioxide can be dispersed in the deacetylated chitin solution.Basic pigments should be avoided. The ratio of deacetylated chitin tosolid may vary over wide limits, from 5 to 25 per ings. For examplaanaqueous dispersion comcent based on the pigment frequently beingdesirable, the preferred amount varying with the particular pigment andother properties desired. Concentraton of pigment may be varied fromthat in a fiat wall paint, 1. e., 40 to 50 per cent, to whatever lowervalue is desired.

Results similar to those described in Example IV were obtained withprimed and unprimed panels painted with white lead in oil. In theseexperiments, however, the faces of the panels were exposed to severeatmospheric conditions outdoors while the backs of the panels wereexposed to a humid atmosphere. Such improvement in blistering resistanceis especially evident with paints having as a vehicle a drying oil or adrying oil modified natural or synthetic resin and, as the pigment, azinc oxide-free system containing a titanium and/or lead pigment, suchas titanium oxide and basic carbonate white lead. Specific examples ofsuch paints are the wellknown white lead in oil, barium sulfateextendedtitanium oxide in a 62% linseed oil modified glyceryl phthalate resin,and the zincless oil paint comprising 40 parts by weight of extendedtitanium pigment (75% B9504 and 25% TiOz), basic carbonate white lead 40parts, and asbestine parts, this pigment combination being used with alinseed oil vehicle containing about 8% of a 5-gallon ester gum oroil-soluble phenol-formaldehyde resin.

In the case of low viscosity deacetylated chitin, the process has beendescribed for the most part in terms of 0.5 per cent solutions in aceticacid since this concentration is both economical and very efiective.However, 0.25 per cent solutions are also effective and even 0.1 percent solutions deposit sufiicient priming material to cause noticeableimprovement. While higher concentrations, that is, up to 6.0 per cent oreven more have been used with favorable results, solutions of one-halftoone per cent concentration applied so as to deposit from one-half totwo ounces of deacetylated chitin per 1,000 square feet are preferredwhere improved adhesion as described above is the objective.

While medium or high viscosity deacetylated chitin or mixtures ofvarious grades can be used to promote adhesion of the surface coat, lowviscosity deacetylated chitin is the most practical and generallyeifective for this purpose. This is to be contrasted with the fact,already brought out, that the most effective sealing action againstpenetration of oils and solvents into the wood, and against bleeding ofoil-soluble materials out of the wood, is obtained with medium and highviscosity deacetylated chitin.

The use as primers of deacetylated chitin solutions containing pigmentshas other effects in addition to improving adhesion. These pigmentedsolutions serve as a first paint coat, pro-- viding both sealing andhiding. Penetration of oils and solvents from subsequently appliedcoatings is prevented and bleeding of organic soluble materials from thewood such as asphalt, 'creosote, and resinous constituents is decreasedor entirely prevented.

Deacetylated chitin emulsions of many materials liquid under conditionsof emulsification are effective primers. For example, an aqueousemulsion comprising 20 per cent of a 65 per cent stearic acid modifiedalkyd resin and 2 per cent of medium viscosity deacetylated chitin asthe acetate was very effective as a primer for a short oil modifiedalkyd resin enamel, improving adacetylated chitin emulsions of lowmelting alkyd resins, or of paints or enamels made with drying oilmodified alkyd resins, are in general useful as primers. These emulsionsmay if desired have solids such as pigments, dispersed therein.

I The deacetylated. chitin solutions or disperse systems used in thisinvention may frequently be modified to advantage by inclusion of othermaterials such as wetting agents, softeners, solvents, mildewinhibitors, and chemical reactants. Wetting agents are frequentlydesirable to improve the uniformity of wetting of the base. Excess ofwetting or certain other agents must be avoided when such materials tendto decrease the sealing effect of the deacetylated chitin coating.

When used as a primer or sealer, deacetylated chitin dries rapidly, isnot attacked by alkalies but rather is insolubilized by them, and is notaffected by organic solvents. When the deacetylated chitin is used inthe grade and amount to form a perceptible film, this film is toughrather than brittle and does not become sticky or tacky from moisture.

As previously indicated, the advantages of the present invention aremost evident where the finish coat consists of or comprises afilm-forming polyhydric alcohol ester of drying oil acids, e. g., adrying oil (raw or bodied), a drying oil modified alkyd resin, or avarnish made by blending a drying oil with a natural or synthetic resin.However, it is within the scope of my invention to use as the top coatany organic film-forming material such as resinous polymers ofmonohydric alcohol esters of alpha-methylene monocarboxylic acids (e.g., ethyl acrylate and methyl alpha-methacrylate) vinyl resins such asvinyl chloride and vinyl acetate, chlorinated rubbers, phenol-andurea-formaldehyde resins, and cellulose derivatives such asnitrocellulose, cellulose acetate and ethyl cellulose. Any of thesesubstances may be suitably plasticized and pigmented, as desired.

In improving the adhesion of coating compositions, particularly whitelead in oil, alkyd resin coatings and especially short oil modifiedalkyd resin coatings, deacetylated chitin is unique in that compositionscontaining it are almost the only materials of many dozens tested whichshow this property. Zinc-oxide-free oil paints are caused to adhere towooden surfaces particularly well, such typical paints being thosecontaining basic carbonate white lead, or titanium pigments, such asmetallic titanates and titanium oxide, alone or extended with such materials as barium sulfate, calcium sulfate, or siliceous material.

By the term alkyd resin coating ismeant a. coating comprising thewell-known drying oil modified alkyd resins made by methods known in theart, one such method being the reaction of drying oil acids withglycerol and phthalic anhydride as described by Kienle, U. S. Patent1,893,873. By short oil alkyd resins are meant those containing 50 percent or less of drying oilone such resin containing, for example, 34.7per cent of linseed oil and 13.9 per cent of Chinawood oil and beingmade from the quantities of glycerol, phthalic anhydride, and acids ofthe two oils calculated to give a final product of this oil content. Bylong oil modified alkyd resins are meant those having more than 50 percent of drying oil in the resin, e. g., that containing 62 per cent oflinseed oil and made from glycerol,

hesion and decreasing blistering. Aqueous de-phthalic anhydride andlinseed oil acids.

The finish coat may in some instances be an aqueous system containingthe organic flimforming material, e. g., an aqueous emulsion of a paint.

In order to promote drying and insolubilization of the deacetylatedchitin priming coat, it may be heated or chemically treated, as withammonia, alkali, alum, formaldehyde, anhydrides, acetic anhydride,ketene, acetyl chloride, or other compounds which react with thealcoholic and amino hydrogen atoms in the deacetylated chitin. Heatingis a preferred method because of simplicity and effectiveness. Where theterm deacetylated chitin is used in the claims without a recitationindicative of the material being in solution, the term includesderivatives, for example, the insolubilized formaldehyde treated, theacetic anhydride or acetyl chloride treated, etc., derivatives and thelike.

The above description and examples are intended to be illustrative only.Any modification of or variation therefrom which conforms to the spiritof the invention is intended to be included within the scope of theclaims. I

I claim:

1. A product comprising a rigid fibrous cellulosic material having apriming coat thereon comprising deacetylated chitin and over saidpriming coat a water-impermeable surface coating of an organicfilm-forming material.

2. A product comprising a rigid fibrous cellulosic material havingaprimary coat thereon comprising deacetylated chitin and over saidpriming coat a water-impermeable surface coating comprising afilm-forming polyhydric alcohol ester of drying oil acids. a

3. A product comprising a rigid fibrous cellulosic material having apriming coat thereon comprising deacetylated chitin and over saidpriming coat a water-impermeable surface coating of a white lead in oilpaint.

4. A product comprising a rigid fibrous cellulosic material having apriming coat thereon comprising deacetylated chitin and over saidpriming coat a water-impermeable surfacecoatingofadryingoilmodiiiedalkydrcsiri.

5. A product comprising wood having a priming coat thereon comprisindeacetylated chitin and over said priming coat a water-impermeablesurface coating of an organic film-forming material.

6. A product comprising wood having'a priming coat thereon comprisingdeacetylated' chitin and over said priming coat a surface coatingcomprising a 'filrn-forming polyhydric alcohol ester of drying oilacids.

7. A productcomprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a zinc oxide free, pigmented, flimforming polyhydric alcoholester of drying oil acids.

8. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a titanium pigmented, film-forming polyhydric alcohol esterof drying oil acids.

9. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a zinc oxide'free, titanium pigmented, film-forming polyrdric alcohol ester of drying oil acids.

10. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a film-forming polyhydric alcohol ester of drying oil acidspigmented with basic car bonate white lead.

11. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coating of awhite lead in oil paint.

12. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a drying oil modified alkyd resin.

13. A product comprising wood having a priming coat thereon comprisingdeacetylated chitin and over said priming coat a surface coatingcomprising a drying oil.

- GORDON D. PATTERSON.

